Manufacturing of integrated circuits has been enabled by high-performance spin-on organic polymeric resists. In addition to sensitivity and resolution requirements, resists must maintain critical linewidth control throughout the patterning process, including both imaging and subsequent transfer via processes such as plasma etch. For example, line-edge roughness on the order of 5-10 nm is a concern at 250 nm, but can render a lithographic process unworkable when critical dimensions fall to below 100 nm.
Until the late 1980s, the radiation sources used in lithographic processes were high-power mercury lamps, first at 436 nm and then followed by 365 nm. Then the transition took place to the krypton fluoride excimer lasers at 248 nm, and more recently to the argon fluoride excimer lasers at 193 nm, and eventually to molecular fluorine lasers at 157 nm. Mass-produced semiconductor manufacturing entered the era of nanopatterning with UV optical lithography when the smallest feature sizes crossed the 100-nm threshold. In the last two years advanced devices have had their half-pitch at 90 nm using 193-nm dry exposures, and it is widely expected to extend to 45-nm half-pitch by incorporating liquid immersion. Indeed, according to the international roadmap for semiconductors (ITRS), this trend will continue unabated for at least one more decade with expected resolution decreasing to 45 nm in 2010, and 32 nm in 2013. Accordingly, a need exists to develop future imaging technologies such as extreme ultraviolet (EUV) lithography or maskless electron beam.
One alternative to conventional projection optical lithography is EUV lithography, when extremely small wavelength photons (13.4 nm) are employed in imaging. It is thought that EUV will be employed to 32-nm nm half-pitch and possibility down to 25-nm nm half-pitch when finally developed. One difficulty with EUV is the lack of a high power photon source, which will limit the manufacturing throughput without the introduction of very high sensitivity resists. To get high-throughput EUV systems, the laser source must be improved to generate more of the extreme ultraviolet radiation, or light. Today's best YAG lasers generate only about 10 Watts of radiation. The power level must be boosted to 100 Watts or more for high-throughput commercial production. Even at this power level, resist sensitivity must improve significantly.
A second alternative to conventional projection optical lithography is maskless electron beam lithography, due to its intrinsically high resolution. The limitation of electron-beam lithography is, however, its relatively low throughput. Until recently, this limitation far outweighed cost considerations of optical projection systems and photomasks. However, the balance is beginning to tilt in the other direction, both because optical lithography is becoming increasingly expensive and because novel concepts of electron-beam systems may significantly boost their throughput. Enhanced throughputs may be sufficient to enable prototyping at reduced cost and turnaround time, and even enable cost-effective production of low-volume (<1000 wafer) device runs. Electron-beam lithography can be looked at as a replacement or an alternative for advanced lithographic technologies such as hyper-NA 193-nm or EUV lithography that may be unavailable or not cost effective for low volume device producers. Nonetheless, for maskless electron-beam lithography to be successfully utilized in integrated circuit fabrication, resist sensitivity will have to be significantly increased.
Accordingly, a need exists for resist formulations and components thereof that will increase the resist sensitivity to imaging lithographic radiation. As well, it is advantageous to achieve such increases in sensitivity without substantial losses in linewidth roughness.